EASIN - European Alien Species Information Network

Stefano PIRAINO
8/7/2018 12:30 PM

Filellum serratum was first described from Cuba by Clarke (1879: 242, as Lafoea serrata), and specifically diagnosed through the adnate part of the hydrotheca “ornamented with a number of ridges or thickened elevations of the perisarc on the outer side”. Based on the original description Stechow (1923, p.145) reported sterile colonies of F. serratum from the gulf of Naples as a new species for the Mediterranean. This perisarcal feature has been considered the main characteristic of the species. However, some related species, such as F. antarcticum, F. magnificum and F. nitidum all have identical striated hydrothecae, but significantly differ in the structure of their reproductive structures (coppinia). Ritchie (1911) was the first author to describe the coppiniae of F. serratum, subsequently figured by Millard (1975: 179, fig. 2C). The first valid record of F. serratum in the Mediterranean supported by description of reproductive structures was from Chafarinas Islands (Peña Cantero et al. 1998). According to Marques et al. (2011) previous records not including description or illustration of the coppinia should be therefore not used to inferring the distribution of the species. The distribution of F. serratum as based on the available literature may be therefore overestimated. Currently, the genus Filellum in the Mediterranean Sea is represented by three species, namely F. disaggregatum, F. serpens and F. serratum, with F. serratum as the only species reported so far bearing minute corrugations over the upper surface of the adnate part of the hydrotheca. However, the hypothesis of additional Filellum species bearing the hydrothecal external transverse ridges cannot be rejected. Due to such taxonomic uncertainty, F. serratum in the Mediterranean should be better regarded as CRYPTOGENIC unless molecular studies will clarify its biogeographical origin and current world distribution. References Clarke, S.F. (1879) Report on the Hydroida collected during the Exploration of the Gulf Stream and Gulf of Mexico by Alexander Agassiz, 1877-78. Bulletin of the Museum of Comparative Zoölogy at Harvard College, in Cambridge, 5, 239–252 Marques, A.C., A.L. Peña-Cantero, T.P. Miranda & A.E. Migotto. 2011. Revision of the genus Filellum Hincks, 1868 (Lafoeidae, Leptothecata, Hydrozoa). Zootaxa, 3129: 1-28. Millard, N.A.H. (1975) Monograph on the Hydroida of Southern Africa. Annals of the South African Museum, 68, 1–513 Pena Cantero, A.L., Garcia Carrascosa A.M. & Vervoort W. (1998) On the species of Filellum Hincks, 1868 (Cnidaria: Hydrozoa) with the description of a new species. J. nat. Hist. 32(2): 297-315 Ritchie, J. (1911) Hydrozoa (hydroid zoophytes and Stylasterina) of the 'Thetis' expedition. Memoirs of the Australian Museum, 4, 807–869. Stechow, E. 1923. Zur Kenntnis der Hydroidenfauna des Mittelmeeres, Amerikas und anderer Gebiete. II. Teil. Zoologische Jahrbucher, Abteilung fur Systematik, Geographie und Biologie der Tiere 47: 29-270.

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